1. Field of the Invention
The present invention relates to an optical fiber fusion splicer that abuts the respective end surfaces of two optical fibers that are to be spliced against each other and fusion splices these optical fibers by heating the abutment portion by arc discharge, and to a method for estimating a shape of a beam which is discharged by the optical fiber fusion splicer.
2. Description of the Related Art
Optical fiber fusion splicers first abut the respective end surfaces of two optical fibers that are to be spliced against each other and then fusion the two end surfaces by heating the abutment portion by arc discharge, resulting in the two optical fibers becoming fusion spliced. In this optical fiber fusion splicer, in order to be able to always make a stable splicing with little splice loss, it is essential that both of the end surfaces of the two optical fibers being spliced are heated uniformly. Namely, it is necessary that the two optical fibers be set such that the discharge beam is applied equally to both optical fibers. Therefore, conventionally, first a central position of the discharge beam is estimated and the optical fibers are abutted against each other in accordance with that position.
The following conventional methods are known as methods for estimating the central position of a discharge beam. In the first method, the distal ends of a pair of discharge electrodes that generate arc discharge in order to melt and thereby fusion splice the end surfaces of the optical fibers are observed, and the observer estimates the discharge central position on the supposition that the discharge central position is positioned over a straight line between the two distal ends.
In the second method, after two optical fibers have been abutted against each other between discharge electrodes, an arc discharge is generated for a set time so that the respective distal ends of the two optical fibers are melted by the heat therefrom. At this time, the positions of the distal ends of the optical fibers regress due to the surface tension created by the melting of the distal ends. Because it would appear logical that the amount by which they regress corresponds to the amount of the melting, namely, to the amount of the heating, the amounts that the distal ends of the two optical fibers regress are measured and the center position is estimated by calculating the central position of the discharge beam relatively from the difference in the regression amounts.
In the third method, after the respective end surfaces of the two optical fibers being spliced have been abutted against each other, the abutment portion is heated by arc discharge causing both end surfaces to melt and the two optical fibers to thus be fusion spliced. At the time of this discharge, an image of the discharge beam is picked up and the brightness distribution on one line in a direction crossing a direct line between the discharge electrodes is estimated, and the central position of the discharge beam is estimated from the brightness distribution (Japanese Patent Application, First Publication No. 2-28605).
However, all of the above conventional methods have the following problems. In the first method, while it is necessary to observe the distal ends of the discharge electrodes, this cannot be done with a device in which the distal ends of the discharge electrodes cannot be observed due to the structure of the optical fiber fusion splicer. In a normal optical fiber fusion splicer an image pickup device such as a TV camera is provided for observing the abutment portion. However, this image pickup device is for observing the abutting optical fiber distal ends and observing whether they are aligned and the like, and in many cases the electrode distal ends are outside the field of vision and an image thereof cannot be picked up. Moreover, even if the electrode distal ends can be temporarily observed, if foreign substance such as dust is stuck to the distal end of an electrode or if the distal end is worn and the shape thereof is not uniform, then the actual shape of the discharge beam becomes irregular so that it cannot be guaranteed that the straight line between the distal ends of the discharge electrodes will be in the center of the discharge beam. Therefore, even if the optical fibers are abutted against each other in a position that has been estimated in this way, it is not possible to heat the distal ends of both optical fibers equally.
In the second method, before the two optical fibers are actually fusion spliced, because the distal ends thereof are first heated and the regression amounts measured, it is not possible to simply reheat the distal ends to perform the fusion splicing. If the distal ends are melted so that they become rounded and then regress, it is necessary to cut off the melted distal ends and to perform the splicing by heating and melting a new cut end surface. Therefore, it is necessary to perform the processing (i.e. removal of the covering, cleaning, and cutting) of the end surfaces of the two optical fibers twice: once for the measuring of the regression amount and once for the fusion splicing, creating the problem of extended time and labor. Moreover, if the discharge is too weak, the distal ends of the optical fiber do not melt sufficiently, resulting in the regression amount difference becoming indistinct and it not being possible to accurately estimate the discharge central position. In contrast, if the discharge is too strong, then both distal ends of the optical fibers become over melted which also results in the regression amount difference becoming indistinct and it not being possible to accurately estimate the discharge central position.
In the third method, because the discharge central position is estimated during the discharge for the fusion splicing, it is not possible to ascertain the discharge central position prior to the discharge for the fusion splicing. Because it is assumed that the discharge central position estimated at the time of the discharge for the previously performed fusion splicing is the same as for the current fusion splicing, if that assumption is not true, then this method is no longer applicable and the quality of the splicing cannot be guaranteed even if the abutment position of the current optical fibers is aligned with the previously estimated discharge central position. Furthermore, because in the third method, the brightness distribution on one line in the picked up discharge beam image is measured so as to estimate the discharge center, there is no way to deal with cases such as when the discharge beam state is slanted or distorted by deterioration of the electrode distal ends or by a condition of dust adhesion, and an accurate central position cannot be estimated.
Moreover, if the image of the discharge beam is observed in a state in which the optical fibers are placed inside the discharge area, a difference is generated between the brightness of the portion where the optical fibers are present and the brightness of the portion where the optical fibers are not present. In addition, if dust or the like adheres to the optical fiber, the brightness of that portion alone changes markedly resulting in the discharge central position being erroneously estimated.
In view of the above circumstances, it is an object of the present invention to provide an optical fiber fusion splicer that has been improved to the point where it allows a discharge central position to be accurately estimated without requiring added labor or time, and allows both distal ends of the two optical fibers being spliced to be heated equally and to perform the fusion splicing with a low level of splice loss.
It is a further object of the present invention to provide a discharge beam estimating method in which the shape of the discharge beam in an optical fiber fusion splicer is estimated resulting not only in it becoming possible to control the splice loss within a low level, but also in it being possible to detect abnormalities such as electrode deterioration, dust adhesion and the like.